Patent GB-744125-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: MERCER RICHARD
IPC: H04Q3/42
Filed: 1950-05-31
Abstract: 744,125. Exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 29, 1951 [May 31, 1950], No. 13538/50. Class 40 (4). The system described in Specification 744,121 is provided with PBX facilities. Parts common to the two Specifications bear the same references. As in the Specification referred to a calledline is tested without operating any numerical switches in the conversational train. A line in a PBX group of lines may be called either by the PBX group number or by an individual number. Different lines of a PBX group may be connected to switches in different numerical stages of the switch train. A line A in final selector 4D, Fig. 2, is provided with PBX lines A+1, A+2 and corresponding switch relays 4DA+1, 4DA+2. When a number is dialled at a calling station CLE and the last digit A is stored by relay 4DRA in the fourth digit responder 4DR, digit counting relay IS4 connects the test lead BTFF to 4DR through responders 1DR, 2DR, 3DR and a busy relay BR. If the line A is free, neither the line relay nor the cut-off relay in equipment WLEA is operated, no busy marking appears on BTFF at instant A and relay IRT operates to start route selection by connecting battery to the common test lead CTL. The responders are released when relay OS operates in series with 4DA in the final selector and is followed by the breakdown relay BD. If the line A is busy, it is marked on BTFF, relays BR, PXA operate in series and BR disables IRT. Relay PXA connects idle-marking leads A+1E, A+2E to BTFF if lines A+1, A+2 2 are idle. The first free.line, say A+ 1, is selected by operation of 4DRA+1 over BTFF at instant A+1, BR is unlocked and IRT operates to complete the connection to PBX line A+ 1. If all the lines A, A+ 1, A+2 are busy, BR remains operated until instant A+3 when the breakdown relay BD operates in series with a relay DIR (not shown) in the busy feed equipment BF which connects busy tone. A numbered line such as XXX2 may be arranged to respond to the PBX number for line XXXA by allotting both line equipments WLE2, WLEA+ 1 to the same line XXX2 and by adding a marking lead A + 1B to the lead 2B on relay 4D2. The line may then be called either as a PBX line with number XXXA or as an independent line with number XXX2. In Fig. 3 (not shown), three lines numbered 1, 2, A in one final selector are grouped with lines A+ 1, A+2, A+3 respectively, additional to the normal A lines, to form three PBX groups of two lines each. In Figs. 4a, 4b, 4c arranged as shown, 10 PBX lines are allotted to a particular number, 1, in final selector 4D, although only seven, PXL1-PXL7, are shown. The PBX lines do not appear in the final selector in which the number appears. If line 1 in selector 4D is busy when tested, a hunting switch PXLH is seized by a digit selector 3D in the previous stage. The switch PXLH in route Pp has access to two PBX lines PXL1, PXL6. Hunting switches in different routes have access to lines, as shown in Fig. 5a. The route Pp is marked busy over operated contacts of relays BR1, BR6 if both lines PXL1, PXL6 are busy. A route is selected giving access to a hunting switch with a free PBX line. When the line 1 tests busy, relays PX1, BR operate in series and 1RT is short-circuited. In the final selector AX follows PX1 and allows testing of PBX lines on only one number at once. If a call arrives for another PBX number in the same final selector, testing is delayed until the next cycle. At instant A+ 1 relay 3DRA + 1 operates over BTFF and a contact of PX1 and unlocks 3DRA previously operated to give access to 4D. Selector relay 3DA + 1 is marked and the conditions of the lines PXL1, PXL6 to which it gives access are marked on TL4D over TLPX. In the meantime, relay AX replaces the busy marking on line 1 with battery at 1B. Relay IRT operates and battery is connected to the common test lead CTL to make the route test. If route Pp is selected, relay 3DA +1 operates and extends the speaking leads SL to the hunting switch PXLH which selects the first idle line PXL1 or PXL6 and completes the connection. The responders are released when breakdown relay BD pulls up at instant A+4. If all the PBX lines are busy, relay ALB operates and disconnects the lead A+1E and responder relay 3DRA+1 does not operate. With larger groups of lines the hunter PXLH nay have three relays and additional relay such as 3DA+1, 3DRA + 1 may be provided in earlier stages. Reference has been directed by the Comptroller to Specifccations 656,559 and 665,129.